Conventionally, there is known a robot hand device equipped with a plurality of finger mechanism mimicking a human hand, and a hand body connected with the finger mechanisms (for example, refer to Patent Document 1). The finger mechanisms of the robot hand device of Patent Document 1 are bent and stretched by a fluid pressure transmission device. The fluid pressure transmission device is equipped with a plurality of driven fluid pressure cylinders provided inside the hand body, and a plurality of driving fluid pressure cylinders provided outside the hand body and respectively connected to the driven fluid pressure cylinders via fluid pressure transmission pipes.
When fluid pressure is generated by the driving fluid pressure cylinder with a driving source such as a motor, the fluid pressure is applied to the driven fluid pressure cylinder connected to the driving fluid pressure cylinder. Thereafter, a piston of the driven fluid pressure cylinder advances and retreats, and a movable member as a constituent element of the finger mechanism connected to the piston moves. As such, with the advancing and retreating of the piston of the driven fluid pressure cylinder, the bending and stretching operation of the joints of the finger mechanism is performed.